INVESTIGATION OF THE FRACTURE HEALING AND MECHANISM OF ASPHALT BINDERS
The self-healing properties of viscoelastic asphalt materials have been widely recognized among pavement researchers which can result in extended service life of asphalt pavements. The study of asphalt healing has mainly fallen into two categories: (1) study the phenomenological behavior of healing and the factors that affect healing; and (2) study the fundamental mechanisms of healing. This research evaluates the self-healing properties and mechanism of asphaltic binders from both macroscopic and microscopic perspectives. It starts with the visualization of the healing phenomena using Field Emission Scanning Electron Microscopy (FESEM) and then studies the fracture healing properties of asphalt binders during damage-healing process. When asphalt binder is subjected to cyclic loading, deformation and fracture may develop simultaneously until fatigue failure. Also, healing (of fracture damage) may happen in conjunction with the recovery of viscoelastic deformation, making the analysis of healing complicated. To characterize the fracture healing properties of asphalt materials, this study presents an analytical method to evaluate the evolution of strain component caused by deformation and fracture during a fatigue process, and separates the contribution of viscoelastic recovery and fracture healing during a rest period. Applying the proposed methodology, the effect of two popular Warm Mix Asphalt (WMA) additives (Sasobit/Evotherm) on fracture healing properties of asphalt binders is studied. Furthermore, the molecular investigation of healing mechanism is followed using the open-source code software LAMMPS (Large−scale Atomic/Molecular Massively Parallel Simulator). The mechanism of diffusion is investigated and found that healing increases with the temperature. Different models are built to study the effect of crack width on healing. The increased mechanical properties (density, bulk modulus, etc.) of the systems after healing determined in Molecular Dynamics simulation substantiates the mechanical fundamentals of the healing phenomena as found in macroscale evaluation. This research will provide significant contribution to the advancement of the healing study by recognizing the fracture healing of asphalt binders and developing preliminary study of healing mechanism using molecular dynamics simulation.